Embodiments herein generally relate to printing systems and methods that use toner and more particularly to a system and method that observes the statistical distribution, for different levels of the transfer field, of mass per area of toner remaining on the drum or belt as the drum/belt transfers the toner. The distribution is compared to predetermined standards and/or other networked printing systems to evaluate characteristics of the toner.
Embodiments herein are equally useful with a drum photoreceptor (or dielectric), as with a belt (photoreceptor or dielectric), and other similar devices. Photoreceptor based engines use light to discharge areas and create the latent image, where the latent image is the charge pattern corresponding to image, while dielectic based engines write the latent image directly onto dielectric. Toner properties can drift over time in a printing engine, negatively impacting system performance, latitude, and print quality stability. In order to maintain stable performance, a printing engine uses process control schemes employing optical density sensors as well as other types of sensors (color engines may have multiple toner control sensors and optical density sensors). Improvements in the measurement of the toner state would enable more advanced control schemes that could result in improved print quality and stability (over time, station to station, and engine to engine including printers having multiple marking engines within one printer or a group of printers networked into a cluster).
Thus, embodiments herein comprise systems that are adapted to monitor toner in a printing engine. The systems include a first device, such as a drum or a belt (which is sometimes referred to herein as a drum/belt) containing a latent image (charge pattern), and a toner source adapted to supply toner to develop the latent image on the drum/belt. A surface such as a transfer belt or printing medium is adjacent to (and/or in contact with) the drum/belt and transfer of the toner from the drum/belt to the surface is achieved by generating a transfer field through the operation of a charged, biased transfer device.
While the drum/belt is designed to transfer all of the toner to the surface, in reality, a small amount of toner remains on the drum/belt and, therefore, the drum/belt sometimes transfers less than all of the toner to the surface. To detect the amount of toner that remains on the drum/belt, embodiments herein place a toner area coverage sensor adjacent the drum/belt to measure the mass per area of toner remaining on the drum/belt just after the drum/belt transfers toner to the surface. Also a controller is connected to the toner area coverage sensor and to the charged transfer device. The controller controls the toner area coverage sensor to detect the mass per area of toner remaining on the drum/belt as (just after) the drum/belt transfers the toner to the surface, while varying the transfer field generated by the charged transfer device. If, in addition to (or instead of) generating an electric field, the transfer device uses heat or some other type of actuator (e.g. ultrasonic energy) to achieve transfer, then these transfer actuators could also be varied.
A calculator unit is provided to calculate a field detachment distribution based on changes in the mass per area of toner remaining as the transfer field of the charged transfer device is varied. The field detachment distribution is a statistical function of the remaining mass per area percentage versus the transfer field (charge or voltage) which can be plotted as a curve on graph. In addition, a comparator compares the field detachment distribution to a predetermined standard to evaluate characteristics of the toner. The comparator can detect a difference between a mean detachment field and a predetermined mean detachment field. The toner will have specific characteristics at the mean detachment field and, if this value shifts, this indicates that the characteristics of the toner have also shifted.
Similarly, the comparator can detect the difference between a probability density function of the measured field detachment distribution and a predetermined field detachment distribution probability density function. Also, the comparator can detect the difference between a stabilization toner mass per area (remaining after the transfer field reaches a stabilization point where the mass per area is minimized) and a predetermined stabilization toner mass per area; and can detect the difference between an observed maximum transfer field and a predetermined maximum transfer field. Again, the toner will have specific characteristics for a given field detachment distribution probability density function; different characteristics for the different stabilization toner masses per area; different characteristics for the different maximum transfer fields and other similar measures of the field detachment distribution. If any of these values shift, this indicates that the characteristics of the toner have also shifted. In response to changes in the characteristics of the toner, the system can alter the operating parameters of the printing engine.
While the foregoing discusses the system with respect to comparisons with predetermined values and standards, the system can also be utilized with relative comparisons of similarly operating machines. For example, sometimes groups of printing engines will be networked together and some printers use multiple marking engines within a single print engine. The printing from each of the different engines should be consistent so that there is little or no variation from printing engine to printing engine. For such printing networks, the controller can alter the operating parameters of the printing system based on comparisons of the different field detachment distributions of the different printing engines within the printing network. Thus, the controller can monitor toner attributes in a plurality of different printing devices, compare the toner attributes, and alter operating parameters of the printing devices depending upon the comparing of the toner attributes to promote printing uniformity between the different printing devices.
These and other features are described in, or are apparent from, the following detailed description.